The effect of tunnel layer thicknesses on the charging/discharging mechanism and data retention of Si nanocrystal dot floating gate devices was studied. Floating gate memories of Si nanocrystals dots with three different SiO2 tunnel thicknesses were fabricated, the key variable being tunnel oxide thickness. Other parameters which can affect memory properties were carefully controlled. The mechanism of electron discharging is discussed based on differences in tunnel SiO2 thickness. Direct tunneling was found to predominate in the cases of 3-and 5-nm-thick SiO2 tunnel layers. However, Fowler-Nordheim tunneling affects the electron discharging characteristics with thicker SiO2 tunnel layers. Clear characteristics in discharging peak differences could be observed in capacitance-voltage measurements on metal-oxide semiconductors with Si floating nanodot devices. Memory properties also depended strongly on tunnel oxide thickness. (c) 2006 American Vacuum Society.